This 2020 paper by Alexandre Deur is very interesting. "[W]e find that relativistic corrections to the rotation curves of disk galaxies are significant at large galactic radii."
"Relativistic corrections to the rotation curves of disk galaxies" - https://arxiv.org/pdf/2004.05905.pdf
And a blog covering the paper: https://astrobites.org/2020/08/17/the-alternative-to-dark-ma...
Ignoring the relativistic nature and nonlinearity of GR is a very large problem with FLRW and other toy models, but they have become embedded in cosmology to the point where it's heresy to question them.
If gravity wasn't self interacting it wouldn't follow the shortest path that gravity itself creates. Light does follow this path. Gravity would move in different directions and at different velocities to light across the universe which is full of gravitational field if it wasn't self interacting. We have seen zero evidence that gravity does propagate differently to light. In fact ligo and other gravity experiments have only confirmed it's the same.
So gravity is almost certainly self interacting. What does this mean? Well it wouldn't change much at small scales. There's not enough effect at say planetary scales to really notice. But what happens when you have a field self interacting across vast distances and involving vast galaxy sized masses? Well your link looks at this and yes it matches some of the anomaly's we are at large scale.
It's a good theory and I suspect despite being hard to argue against it will face opposition since it means a lot of scientists were chasing a dead end.
They have shown something that is not well accounted for in current theories. Just as MM showed light is always observed travelling at the same velocity Ligo has shown gravity is self interacting. Now we need to change our models and build mathematical frameworks to account for this. It is not acceptable to have a theory that doesn't account for this post Ligo.
But at this point nobody is going to revisit MM, attempting to do so would immediately ruin your scientific reputation.
Wiki has their data: https://upload.wikimedia.org/wikipedia/en/thumb/d/d1/Michels...
In Michelson's own words (per wiki):
> The expected deviation of the interference fringes from the zero should have been 0.40 of a fringe – the maximum displacement was 0.02 and the average much less than 0.01 – and then not in the right place.
The data doesn't look anything like a signal, and wiki also says:
> Roberts (2006) has pointed out that the primitive data reduction techniques used by Miller and other early experimenters, including Michelson and Morley, were capable of creating apparent periodic signals even when none existed in the actual data.
> But subsequent experiments stopped rotating the assembly at all and just relied on the rotation of earth
This is also untrue. Per https://arxiv.org/abs/1002.1284 (found via references in wiki):
> Our measurement compares the resonance frequencies of two orthogonal optical resonators that are implemented in a single block of fused silica and are rotated continuously on a precision air bearing turntable
But when I read it, I found something interesting.
"The final precision could be reached by integrating over more than 130 000 rotations relying on a careful suppression of systematic effects caused by the turntable rotation"
I wondered what effects they were suppressing, and while they discuss that to some extent they also say:
"While even faster rotation would have allowed to acquire more data and thus improve statistics, it resulted in increased residual systematic effects presumably due to modulated centrifugal forces and was thus not implemented"
And they state:
"active rotation potentially causes a systematic modulation of the beat frequency and might thus mimic an anisotropy signal. For exam- ple, gravitational or centrifugal forces that act on the resonators may get modulated with the turntable rota- tion and therefore modulate the length of the resonators."
So I would ask, how do we distinguish between new physics and systematic errors that look like new physics and need to be excluded from the experiment?
The difference between gravitational wave and gamma rays is more dependent on initial magnitude of gravitational wave, than on distance traveled.
The neutron stars are close enough to the black hole that you see multiple images of them, and the images are highly distorted. E.g.: You can see them even when they're "behind" the black hole due to the highly bent path of the light.
You have hundreds of probes scattered over a large volume of space, each equipped with an optical telescope and a gravity wave sensor similar to LIGO.
What would you expect to observe?
Would the frequency of the final "ringdown" chirp before the merger be observed identically in the optical and gravity sensors? Would they be observed as "coming from" the same spots in the sky? Would you expect to feel a higher contribution to gravity by the neutron stars due to their multiple images? Etc...
It's interesting that our intuition about the consistency of the rules related to the speed of causality imply that the answers ought to be: Yes, identical, yes, yes, etc...
But that means that gravity is definitely self-interacting, and it also means that gravity can be focused, just like light can be focused by gravitational lensing.
This implies that stars at the edge of a galactic disk "see" more gravity from the opposite side of their galaxy due to the lensing effect of the central bulge!
I don't know if this is the right way to think about this. Gravity follows all paths. In a sense, it is the path. Or, as Hawking described it[0]:
> [Gravity] shapes the arena in which it acts, unlike other fields which act in a fixed spacetime background.
Back to your comment:
> So gravity is almost certainly self interacting.
I'm confused by the "almost certainly". I think this has long been established[1], but for entirely different reasons: The Einstein field equations are highly non-linear, so of course there will be self-interaction.
Or, if you prefer to think of the Einstein-Hilbert action: The Lagrangian density L = R · sqrt(det|g|) behaves as L ~ g⁻¹ · Ric · g², and the Ricci tensor is Ric ~ (∂g)∂(g⁻¹) + g⁻¹ ∂²g + (g⁻¹)²(∂g)², so if we view gravity as a quantum field theory (effective or whatever), there are plenty of self-interaction terms that will prevent the N-point function from vanishing for N > 2. Already in the weak field approach (where you approximate g = 1 + h) you get a triple graviton vertex, see p. 21 of https://arxiv.org/abs/1702.00319 .
Maybe we are talking about different definitions of "self-interaction here"?
[0]: Hawking: The Nature of Space and Time (1994), https://arxiv.org/abs/hep-th/9409195
[1]: See e.g. https://physics.stackexchange.com/questions/293873/do-gravit...
It really is a beautiful theory if correct